Central Italy, winter 1944. The war leaves its trail of desperation, murderous crimes, pillaging and abandoned towns.A peculiar group of animals wanders around the devastated countryside, getting by with their wits: Boldsteed, a middle-aged Sicilian horse with a strong build and a generous heart; an American Army dog called Jack and his inseparable bee-pilot Bee-17; Aurelia, a cat from Rome with an amazing talent for getting out of the stickiest situations; and lastly Christopher, the irksome and long-winded rooster from Tuscany.The group's vagabond existence is disrupted when they encounter a small, seven-year-old shoeshine boy with a bewildered expression. The young lad has miraculously survived an air raid and because of the shock he can no longer speak, apart from repeating the same two words: "Boom! Boom!"... and this is the name the animals give him.The band of five decides to take Boom Boom onboard and reunite him with his family. Their only clue is a fragment of a photograph showing the boy with his parents. The adventure will be bristling with obstacles and difficulties, and the group will cement their friendship and team spirit. But they will also experience fear, hunger, cold, and the bitterness of betrayal... until the happy ending when Boom Boom is reunited with his family thanks to the help of his friends.
The difficult and treacherous path also represents an interior journey travelled by each of the characters, who will in the end discover a deeper awareness of their own existence.